The present invention relates generally to a hydraulic anti-skid device for use in a hydraulic braking system of a vehicle.
As is well known in the art, a hydraulic anti-skid device of this type is usually provided in a passageway supplying a hydraulic fluid pressure from a master cylinder to brake units such as wheel cylinders and controls the supply of the hydraulic fluid pressure to the brake units in response to, for example, an electronic signal and a hydraulic fluid pressure which is produced based on the pump pressure of a pump by a regulator valve.
In the event of braking of a vehicle being effected by depressing a brake pedal thereof, when it is unnecessary to reduce the hydraulic fluid pressure fed to the brake unit as when the deceleration of the vehicle is not excessively great, the anti-skid device allows the hydraulic fluid pressure from the master cylinder to pass to the brake units. Conversely, when it is necessary to reduce the hydraulic fluid pressure fed to the brake units as when the deceleration of the vehicle is excessively great, a predetermined electronic signal is generated and the anti-skid device prevents the hydraulic fluid pressure from the master cylinder from being fed to the brake units and simultaneously reduces the pressure prevailing in said brake units.
Also, when the hydraulic fluid pressure from the pump is not fed because of any trouble, the anti-skid devices provides communication between the master cylinder and the brake units irrespective of the presence and absence of the electronic signal. Such a hydraulic anti-skid device is in detail described later in connection with FIG. 1 of the accompanying drawings.
It is, therefore, an object of the invention to provide a hydraulic anti-skid device for a hydraulic braking system of a vehicle, which is capable of purging air in the braking pressure circuit of the anti-skid device without running the engine of the vehicle and without providing the anti-skid device with means for purging air, and which is capable of feeding the braking pressure from the master cylinder to a brake unit to ensure the braking operation when the hydraulic fluid pressure is not generated by the pump without providing a bypass valve and a differential valve provided in a conventional device so that the anti-skid device is simplified in construction and is reduced in size and weight.
This object is accomplished by providing locking means for locking the expansion valve of the anti-skid device in a position in which the expansion valve provides communication between the master cylinder and a brake unit when the engine does not run or hydraulic fluid pressure is not generated by the pump so as to have the expansion valve perform the function of the bypass valve and the differential valve of the conventional device as well as the function inherent in the expansion valve.